Micro-fluid ejection devices, such as ink jet printers continue to evolve as the technology for ink jet printing continues to improve to provide higher speed, higher quality printers. However, the improvement in speed and quality does not come without a price. The micro-fluid ejection heads are more costly to manufacture because of tighter alignment tolerances.
For example, micro-fluid ejection heads were made with nozzle members, such as nozzle plates, containing flow features. The nozzle plates were then aligned, and adhesively attached to a substrate. However, minor imperfections in the substrate or nozzle plate components of the ejection head or improper alignment of the parts may have a significant impact on the performance of the ejection heads. For the purposes of this disclosure, the term “substrate” is intended to include, but is not limited to, semiconductor substrates, silicon substrates, and/or ceramic substrates suitable for use in providing micro-fluid ejection heads.
One advance in providing improved micro-fluid ejection heads is the use of a photoresist layer applied to a device surface of the substrate as a thick film layer. The thick film layer is imaged to provide flow features for the micro-fluid ejection heads. Use of the imaged thick film layer enables more accurate alignment between the flow features and ejection actuators on the device surface of the substrate.
While the use of an imaged photoresist layer improves alignment of the flow features to the ejection actuators, there may still exist alignment problems associated with the nozzle plate. Misalignment between the ejection actuators and corresponding nozzle (e.g., holes) in a nozzle plate attached to the thick film layer has a disadvantageous effect on the accuracy of fluid droplets ejected from the nozzles. Ejector actuator and nozzle hole alignment also has an effect on the mass and velocity of the fluid droplets ejected through the nozzles.
Conventional photoresist layers used for the thick film layer are derived from components that affect the properties and characteristics of the thick film layer once the layer is imaged and developed. For example, conventional photoresist layers are subject to developing stress cracks, imperfections, and distortions that reduce adhesion between the thick film layer and the nozzle plate attached to the thick film layer. Accordingly, there is a need for, for example, improved photoresist or photoimageable materials that provide enhanced characteristics and dimensional stability for use in micro-fluid ejection head structures.
Amongst other embodiments of the present invention, there is provided a thick film layer for a micro-fluid ejection head, a micro-fluid ejection head, and a method for making a micro-fluid ejection head. One such thick film layer includes a negative photoresist layer derived from a composition containing a multi-functional epoxy compound, a difunctional epoxy compound, a photoacid generator devoid of aryl sulfonium salts, an adhesion enhancer, and an aryl ketone solvent. The negative photoresist layer has increased planarity subsequent to photoimaging and developing the photoresist layer.
In another embodiment there is provided a method for increasing the planarity of a surface of a thick film layer after photoimaging and developing flow features therein for a micro-fluid ejection head. The method includes applying a negative photoresist layer adjacent (e.g., to) a device surface of a substrate. The negative photoresist layer is derived from a multi-functional epoxy compound, a difunctional epoxy compound, a photoacid generator devoid of aryl sulfonium salts, an adhesion enhancer, and an aryl ketone solvent. The photoresist layer is imaged and developed to provide the flow features therein, wherein the thick film layer has a substantially planar thick film layer surface.
In yet another embodiment, there is provided a micro-fluid ejection head including a substrate having a device surface. The ejection head has a photoimaged and developed thick film layer applied adjacent the device surface of the substrate. The thick film layer is a negative photoresist layer derived from a multi-functional epoxy compound, a difunctional epoxy compound, a photoacid generator devoid of aryl sulfonium salts, an adhesion enhancer, and an aryl ketone solvent. Upon imaging and developing, the negative photoresist layer has increased planarity for use in the micro-fluid ejection head. A nozzle member is adjacent the imaged and developed thick film layer.
A further embodiment of the disclosure provides a dimensionally stable thick film layer for a micro-fluid ejection head. The dimensionally stable thick film layer is derived from a difunctional epoxy component having a weight average molecular weight ranging from about 2500 to about 4000 Daltons, a photoacid generator, an aryl ketone solvent, and an adhesion enhancing component. The dimensionally stable thick film layer has a cross-link density upon curing that increases the dimensional stability of the thick film layer sufficient to provide flow features therein having substantially vertical walls.
An advantage of the compositions and methods according to at least some of the exemplary embodiments of the disclosure is that the thick film layer may be made and processed with fewer imperfections. For example, stress cracking of the thick film layer may be reduced. Also, planarity of the thick film layer and resistance to various fluids may also significantly improved over conventional thick film layers. The improved planarity of the thick film layer is effective to provide improved adhesion between the nozzle member and the thick film layer thereby reducing the incidence of delamination that may occur.
Additionally, thick film layers made according to at least some of the exemplary embodiments of the disclosure may exhibit significantly increased dimensional stability during subsequent micro-fluid ejection head manufacturing steps. An increase in dimensional stability of the thick film layer may be achieved by increasing the cross-link density of the thick film layer to a predetermined level. The dimensional stability of the thick film layer may be determined, for example, by observing the amount of deformation of flow features formed in the thick film layer during a step of bonding a nozzle member to the thick film layer. Excessive shrinkage of the thick film layer, which may reduce adhesion of the thick film layer to a substrate, may result if the cross-link density is too high. Accordingly, the compositions described herein may provide suitable thick film layers that provide the desirable stability and adhesion characteristics required for micro-fluid ejection heads.
For purposes of the disclosure, “difunctional epoxy” means epoxy compounds and materials having only two epoxy functional groups in the molecule. “Multifunctional epoxy” means epoxy compounds and materials having more than two epoxy functional groups in the molecule.